Many buildings are provided with exhaust vents to evacuate air from the interior of the building to out-of-doors. Typical examples include exhaust vents for residential driers and stoves.
When the ventilation system operates intermittently, if the exhaust outlet is left in an open condition, a backdraft condition may occur. In cold climates, cold air may enter the structure, causing discomfort, condensation and heat loss.
It would, therefore, be desirable to provide an automatic mechanism for opening and closing an air exhaust outlet, according to whether or not air is being exhausted or ventilated therethrough.
A variety of prior art references have addressed this problem. Some have relied directly on activation of the closure system by the direct means of the physical force that the over-pressure develops when the exhaust fan is turned on. Others have relied on a powered opening mechanism that is coupled directly to the ventilation system's fan or motor. In such cases, the opening mechanism is operated by an electrical switch that is activated by the electrical circuit that turns the fan motor on. Examples in the former category of direct, pressure activated systems are:
U.S. Pat. No. 2,730,943 R. B. Klein PA1 U.S. Pat. No. 2,739,521 W. A. Spear PA1 U.S. Pat. No. 3,541,945 Monroe L. Wexler PA1 U.S. Pat. No. 4,214,380 Stephen T. Meyer PA1 U.S. Pat. No. 4,237,621 Lucien Boismenu PA1 (1) an actuating motor means for positioning said closure in either a closed or open state; and PA1 (2) switch means for activating said motor to position said closure in either said open or closed state PA1 (1) a source of electrical current for said actuating motor means; PA1 (2) electrical switch means capable of switching said current to said motor means between "on" or "off" conditions; PA1 (3) an over-pressure sensor system connected to activate said switch and comprising:
The use of direct mechanical force derived from an over-pressure condition is deficient in that the weight of the closure means, generally a flap or segmented vanes, must be kept to a minimum. This, in turn, limits the amount of closing force that such closure means may exert. Further, variations in the degree of over-pressure, as when temporary blockages or diversions of air occur within the conduit, may cause the closure means to oscillate, and produce noise.
As mentioned above, it is also known to activate the opening and closing of doors by electric actuators in accordance with the activation of the fan motor. This arrangement has the disadvantage of requiring that an electrical connection from the ventilator fan motor to the ventilator outlet be installed.
However, a combined mechanism for conveniently detecting a draft/no-draft condition in an air exhaust outlet, and activating a closure for such a ventilator outlet in a positive fashion without being electrically or mechanically connected to the ventilator fan has not been proposed.
It is, therefore, an object of this invention to provide such a mechanism.